The public advocate is supposed to be the most important post in this city after the mayor. According to the City Charter, if something happens to the mayor, the advocate succeeds him. So it’s telling that according to a recent Quinnipiac University poll, only 20 percent of likely voters in the Democratic primary (the only one that matters, because no Republican is running for the post) could even name a candidate in today’s race.

Some might cite this as an indictment of an ignorant electorate. Our view is that city voters have it exactly right. They appreciate that it’s a farce.

But it’s proving an expensive farce. In the Democratic mayoral primaries, Bill de Blasio is clocking in at more than 40 percent in the polls, enough to avoid a runoff. But none of the five Democratic candidates for public advocate might pull that much. So taxpayers face the prospect of paying millions of dollars to hold a runoff in that race — to determine the winner for a job whose entire office has a budget of $2.25 million.

But if the job of public advocate is so ridiculous, why do so many politicians covet it? The answer is to look at what it’s done for de Blasio. One reason he’s leaped to the top of the mayoral polls is that he’s benefited from four years in a job that gives him no real responsibilities but plenty of opportunities for self-promotion.

All that’s required is that you can write press releases and toot your own horn. And New York is filled with politicians who would love to do just that.

Alas, this office cannot go away without a revision of the City Charter. That’s highly unlikely. In the meantime, The Post will continue to decline to endorse any candidate for public advocate until we find one with the only qualification for that office: a promise to work to abolish it.